# Help with Stoichiometry

a. A sample of CaCO3 decomposes when heated to form calcium oxide and carbon dioxide. 1.5432 g of CO2 are released in the reaction. Find g of CaCO3 in the original sample.
CaCO3 --> CO2 + CaO

1.5432 g CO2*(1 mol of CO2/44.01 g) = 0.035065 mol of CO2*(1 mol CaCO3/1 mol CO2) = 0.035065 mol CaCO3

0.035065 mol CaCO3*(100.09 g/ 1mol CaCO3) = 3.5097 g CaCO3??

b. The original sample was a mixture from which only CaCO3 released carbon dioxide. Calculate the percentage by mass of CaCO3 if original's sample mass was 5.768 g.

Do I divide 3.5097 g CaCO3/5.768 g * 100 or must I subtract the grams of CO2 from the original sample's mass?

Thanks.

Last edited:

Any volunteers?

Thanks again.

Gokul43201
Staff Emeritus
Gold Member
Soaring Crane said:
a. A sample of CaCO3 decomposes when heated to form calcium oxide and carbon dioxide. 1.5432 g of CO2 are released in the reaction. Find g of CaCO3 in the original sample.
CaCO3 --> CO2 + CaO

1.5432 g CO2*(1 mol of CO2/44.01 g) = 0.035065 mol of CO2*(1 mol CaCO3/1 mol CO2) = 0.035065 mol CaCO3

0.035065 mol CaCO3*(100.09 g/ 1mol CaCO3) = 3.5097 g CaCO3??
That's correct.

b. The original sample was a mixture from which only CaCO3 released carbon dioxide. Calculate the percentage by mass of CaCO3 if original's sample mass was 5.768 g.

Do I divide 3.5097 g CaCO3/5.768 g * 100 or must I subtract the grams of CO2 from the original sample's mass?

Thanks.
This looks a little silly, but your first idea seems right.

all seemed right: (3.5097/5.768)*100 should do it.